Field of the Invention
The present invention relates to a developing apparatus that is used in an electrophotographic image forming apparatus.
Description of the Related Art
An image forming apparatus such as a copier or a laser beam printer that forms an image on a recording material using an electrophotographic system forms an electrostatic image (latent image) by applying light corresponding to image data onto an electrophotographic photosensitive member (photosensitive drum) that is uniformly changed by a charging unit. Subsequently, a developing apparatus feeds toner as a developer to the electrostatic image, and the electrostatic image is thereby visualized as a toner image (developer image). The toner image is transferred to the recording material such as recording paper from the photosensitive drum by a transfer apparatus. The toner image transferred to the recording material is fixed onto the recording material by a fixing apparatus.
Japanese Patent Application Laid-open No. H4-31880 describes a developing apparatus in which the surface of a developing roller as a developer carrying member is selectively caused to hold charges and a large number of minute closed electric fields are formed in the vicinity of the surface of the developing roller, whereby toner is fed onto the surface of the developing roller and the developing roller is caused to carry the toner. In addition, Japanese Patent Application Laid-open No. 2014-238568 describes a developing apparatus that is configured such that a guide surface having an inclination angle of at least an angle of repose of toner and less than 90 degrees is provided in an inner wall of a toner storage chamber of a developing container, and the toner slides down the guide surface by its own weight and moves toward the developing roller. According to these configurations, unlike a conventional art, even without providing a toner feed roller for feeding the toner to the developing roller, it becomes possible to feed the toner to the developing roller.
In recent years, due to request from the market, an increase in the capacity of the developing apparatus is desired. However, in the case where the container is designed so as to have a large angle of the inner wall of the container of the developing apparatus in consideration of the maximum angle of repose during use of the toner, the dimensions of the container are increased upwardly in the gravity direction. As a result, a large load is applied to lower toner, the toner having received the load flows in the developing apparatus, and degradation of the toner is thereby accelerated. When the degradation of the toner occurs, a toner attraction effect by the minute closed electric field is reduced. Consequently, image failure is caused by the toner degradation in the latter half of the use period of the developing apparatus, and the convenience of a user may be spoiled.
An object of the present invention is to provide a technique capable of preventing the degradation of the toner and maintaining image quality until the latter half of the use period of the developing apparatus over a long time period while achieving an increase in the storage amount of the toner.